China's military has been the target of a "considerable number'' of cyberattacks, the Defense Ministry said on Wednesday.

Military computers suffered "a large number" of overseas attacks, with "a considerable number" of them originating from the US judging from the IP addresses, said ministry spokesman Geng Yansheng.

Every country should handle cybersecurity in a "professional and responsible way", Geng stressed.

But he did not directly accuse the US government of being behind the attacks as IP addresses can be disguised, he said.

The remarks came in response to a report on Tuesday by US computer security firm Mandiant that accused China's military of hacking US websites.

Cybersecurity is a new way for Washington to levy pressure on the Chinese military, observers said.

The report alleged that a military unit in Shanghai was behind a series of cyberattacks against US companies.

The White House said that the Obama administration has repeatedly expressed its concerns about cybertheft to the highest levels of the Chinese government, and military.

Richard Bejtlich, the chief security officer at Mandiant, said the company decided to make its report public in part to help send a message to both the Chinese and US governments to communicate with each other "without having to worry about sensitivities around disclosing classified information", according to media reports.

"China and the United States have maintained communication over the (hacking) issue," Foreign Ministry spokesman Hong Lei said at a news conference on Wednesday.

The Defence Ministry said Mandiant's report is groundless both factually and legally, and "releasing irresponsible information will not help solve problems".

"The report lacks technical proof as it only relies on linking IP address to reach a conclusion the hacking attacks originated from China," said Geng.

Cyberattacks are global, anonymous and deceptive and their true sources can often be difficult to identify, he added.

Ye Zheng, an information specialist from the People's Liberation Army, said IP addresses do not provide proof of hackers' origins, and it is hard to verify government support behind them.

Reaction among netizens raised the possibility of a disguised IP address.

"If I were to attack a foreign agency it would be undercover with a disguised IP address,'' said "Beijing Gentlemen of The Wind", a Chinese netizen.

Su Hao, a professor of security affairs at China Foreign Affairs University, raised the possibility that competition could be a reason for the US allegations, especially as Chinese information technology has made strides recently.

Experts said recent allegations could be part of an effort by lobbying groups and private companies to push Congress to pass legislation and increase funding for cybersecurity.

Pointing out a "threat'' is a convenient way for Washington to seek an increase in its defense budget and enlarge cybersecurity forces, Hu Xiaofeng, a military commentator, said.

Zhu Zhiqun, a professor of political science and international relations at Bucknell University in Pennsylvania, said that the allegation that China's military is somehow involved in cyberattacks is not entirely new. But "the motives of Mandiant's report are unclear, and the timing is questionable".